Preparation of benzoquinones by oxidation of para-substituted phenols

ABSTRACT

Process for producing substituted benzoquinones through oxidation of para-substituted phenols by manganese dioxide in a mixture of aqueous sulfuric acid and a cosolvent. A typical parasubstituted phenol reactant is 2,6-di-tert-butyl-p-cresol, and its oxidation product is 2,6-di-tert-butyl-p-benzoquinone.

United States Patent Dietl et al. Oct. 24, 1972 i [54] PREPARATION OFBENZOQUINONES 3,213,114 10/1965 Braxton et al ..260/396 R BY OXIDATIONOF PARA- 3,406,188 10/ 1968 Fletcher ..260/396 R SUBSTITUTED PHENOLS3,549,669 12/1970 Clemens ..260/396 R 3 576 016, 4/1971 Finkbeiner..260/396 R 72 I tors. Hans K. Dietl' H d S. Y l 1 both of mngspgn,3,646,073 2/1972 Wollensak ..260/396 R [73] Assignee: Eastman KodakCompany, Primary Examiner vivian Gamer Rmhester, Att0mey C. D. Quillen,Jr. and Donald w. Spurrell [22] Filed: June 10, 1971 211 Appl. No.:151,904 [57] ABSTRACT Process for producing substituted benzoquinones[52] us CL 260/396 R 260/621 R 260/623 R through oxidation ofpara-substituted phenols by man- 260/625; ganese dioxide in a mixture ofaqueous sulfuric acid 511 1nt.Cl ..c07 49/64 and a cosolvem- A typicalPara-substituted phenol 581 Field of Search ..260/396 R reactant is2,fi-di-tert-butyl-p-cresol, and its Oxidation product is2,6-di-tert-butyl-p-benzoquinone. [56] References Cited 5 Claims, NoDrawings UNITED STATES PATENTS 3,065,155 11/1962 Welsh ..260/396 RPREPARATION OF BENZOQUINONES BY OXIDATION OF PARA-SUBSTITUTED PHENOLSThis invention relates to a process of producing pbenzoquinones. Inparticular, this invention relates to a process for producingsubstituted benzoquinones by oxidation of para-substituted phenols withmanganese dioxide.

One of the most formidable problems involved in the preparation ofbenzoquinones is caused by the fact that oxidation routes known in theart lead to extensive byproduct formation. Thus, for example, in theprior art methods, the oxidation of 2,6-di-tert-butylphenol leadsprimarily to 3 ,3 ,5 ,5 -tetra-tert-butyl-diphenoquinone (M. S. Kharaschet al., J. Org. Chem. 22, 1439 (1957). Some of the prior art methods ofpreparing substituted benzoquinones or hydroquinones are based upon thereaction of alkali metal hydroxides with halophenols at hightemperatures. Unfortunately, these processes are not readily applicableto complex phenols and, in particular, are not readily applicable to2,6-dialkylated phenols because the elevated temperatures required leadto extensive rearrangement and decomposition. Another method ofpreparing substituted benzoquinones is the decomposition ofnitrosophenols to benzoquinones (U.S. Pat. Nos. 3,395,160; 3,415,849;3,415,850). This process is cumbersome since the nitrosophenols havefirst to be prepared from the corresponding phenols and then, afterisolation, have to be reacted further. There exists, therefore, a needfor a process capable of converting complex phenols to substitutedbenzoquinones in high yields without extensive contamination withdecomposition products.

Objects, therefore, of the present invention are to provide an improvedmethod for the preparation of substituted benzoquinones; and, inparticular, to provide a process ideally suitable for the preparation of2,o-di-tert-butyl-p-benzoquinone.

These and other objects hereinafter appearing have been attained inaccordance with the present invention through the discovery of theprocess which comprises treating a para-substituted phenol derivativewith manganese dioxide in sulfuric acid as the reaction medium. It isnecessary to use a cosolvent with the sulfuric acid, for example,aliphatic organic carboxylic acid of one to 10 carbons, such as aceticor propionic acids or aliphatic ketones of three to 10 carbons such asmethyl ethyl ketone. The reaction may be carried out at a temperaturefrom about to about 120 C. with 35 to 90C. being preferred. The sulfuricacid may have a concentration in water or from about to about 70% byweight with 30 to 50% being preferred. The amount of aqueous sulfuricacid employed, of course, should be such as to form the necessarymanganese sulfate in the redox reaction. The preferred ratio of organicacid or ketone to sulfuric acid is in the range of 1:10 to 10:1 byweight.

The manganese dioxide employed in the process may be in any form.Beta-manganese dioxide is preferred and a suitable source is pyrolusiteore. The ratio of manganese dioxide to phenol may be in the range ofabout 1:10 to 10:1 on a weight basis. Even higher ratios may be used,since it is possible, for example, to extract the quinone fromunconsumed oxidant. Suitable phenols are any para-substituted phenols,which have at least another group in ortho position. These include 22,4,6-tri-tert-butyl-phenol; 2,4,6-trimethylphenol; 2,6-di-tert-butyl-p-cresol; and 2,4,6-trichlorophenol. Such phenols may berepresented by the general formula wherein R R and R may be the same ordifferent alkyl groups of one to eight carbons, or halogen, and R may bea -COOR group wherein R is hydrogen or alkyl of one to 12 carbons.Para-cresol itself gives only an uneconomically small yield ofbenzoquinone, probably because p-benzoquinone, itself is not stable inthe reaction system.

The following examples further illustrate the invention:

EXAMPLE 1 with ether, and the ether is allowed to evaporate to give 15g. yield) of 2,6-di-tert-butyl-p-benzoquinone.

EXAMPLE 2 This example shows that para substitution is necessary to givegood yield of benzoquinone. A quantity of 20 g. of2,6-di-tert-butylphenol is added to a mixture containing to g. 40%sulfuric acid in water and 75 g. glacial acetic acid. The mixture istreated exactly as described in Example 1. Only 2.1 g. of2,6-di-tert-butylp-benzoquinone (10% yield) is obtained.

EXAMPLE 3 This example shows that in comparison with Example 1, omissionof acetic acid as cosolvent results in lower yields and longer reactiontimes. A quantity of 20 g. 2,6-di-tert-butyl-p-cresol in 200 g. 40%sulfuric acid is oxidized with 40 g. beta-manganese dioxide for 8 hrs.at 60 C. By steam distillation, 3 g. 2,6-di-tert-butyl-pbenzoquinone isobtained. Some starting phenol (1 g.) is recovered.

EXAMPLE 4 This example oxidizes a phenol with a methyl substitution inthe ortho position. A quantity of 20 g. 2,4,6- trimethylphenol isoxidized with 20 g. beta-manganese dioxide in 150 g. 40% sulfuric acidand 75 g. glacial acetic acid for 4 hrs. at 50 C. By steam distillation,5 g. of 2,6-dimethyl-p-benzoquinone is obtained.

This example oxidizes a phenol with a tertiary butyl group in the paraposition. A quantity of 20 g. 2,4,6-tritert-butylphenol is oxidized with40 g. manganese dioxide in 40% sulfuric acid containing acetic acid at60 C. for 18 hrs. Steam distillation of the diluted reaction mixturegives a 70% yield of 2,6-di-tert-b'utyl-pbenzoquinone calculated onconverted starting material.

EXAMPLE 6 This example demonstrates the use of propionic acid as solventand of oxidizing a phenol with a halogen in para position. A quantity of20 g. 4-chloro-2,6-di-tertbutylphenol is oxidized with 40 g.beta-manganese dioxide in 150 g. 40% aqueous sulfuric acid and 75 g.propionic acid for 10 hrs. at 45 C. By steam distillation a 50% yield of2,6-di-tert-butyl-p-benzoquinone and a 25% yield of2,6-di-tert-butyl-3-chloro-p-benzoquinone is obtained.

EXAMPLE 7 This example demonstrates the use of manganese dioxide otherthan the beta form and the possibility of oxidizing a phenol with aphenyl group in para position. A quantity of 20 g.4-phenyl-2,6-di-tert-butylphenol is oxidized with gamma-manganesedioxide in 40% aqueous sulfuric acid containing acetic acid, at 70 C.for 5 hrs. By steam distillation a 60% yield of2,6-di-tertbutyl-p-benzoquinone is obtained.

EXAMPLE 8 Oxidation of 2,6-Di-tert-butyl-p-cresol Using Methyl EthylKetone as Cosolvent A quantity of 20 g. of 2,6-di-tert-butyl-p-cresol isadded to a mixture containing 150 g. of 40% aqueous sulfuric acid and 75g. of methyl ethyl ketone. The mixture is heated to 65 C. with stirringand 40 g. of finely powdered beta-manganese dioxide (py olusite) isadded over a period of 2 hr. at 60 C. After the addition of manganesedioxide is completed, stirring is continued for another 4 hr. at 65 C.Then, after cooling to room temperature, the reaction mixture is dilutedwith 600 ml. water and steam distilled. The distillate is extracted withether and the ether is allowed to evaporate to give 18.3 g. of a mixtureof 2,6-di-tert-butyl-pbenzoquinone and 2,6-di-tert-butyl-p-cresol. Thetwo components are separated by column chromatography (A1 0 hexane aseluant) to give 9.6 g. of 2,6-di-tertbutyl-p-benzoquinone (85% yield onconverted starting material) and 8.7 g. of recovered starting material.

EXAMPLE 9 Oxidation of 3,5-Di-tert-butyl-4-hydroxybenzoic Acid 600 ml.water and steam distilled. The distillate is extracted with ether, andthe ether allowed to evaporate to give 8.6 g. 55% yield) of2,6-di-tert-butyl-pbenzoquinone. Unreacted starting material is left inthe distillation pot in the steam distillation.

EXAMPLE 10 Oxidation of 2,4,6-Trichlorophenol (Chlorine in the ortho andpara positions) A quantity of 20 g. of 2,4,6-trichlorophenol is added toa mixture containing 150 g. of sulfuric acid in water and g. of glacialacetic acid. The mixture is treated as described in the examples above.A 60% yield of a mixture of trichloro-p-benzoquinone (about 3 parts) and2,6-dichlorop-benzoquinone (about 1 part) is obtained.

The benzoquinones produced by this process and the hydroquinones thatcan be produced from them are reactive chemical intermediates and havethe many uses known for these types of compounds. The benzoquinones forexample are easily reduced to hydroquinones and can, therefore, functionin organic reactions as oxidizing agents. The hydroquinones, which caneasily be obtained from the benzoquinones by known methods are useful asantioxidants, or can be converted to antioxidants.

The invention has been described in considerable detail with particularreference to preferred embodiments thereof, but it will be understoodthat variations and modifications can be effected within the spirit andscope of the invention as described hereinabove.

We claim:

1. The process comprising treating a para-substituted phenol of theformula wherein R R and R may bethe same or different wherein R and Rare as defined above, said organic solvent being selected from alkanoicacids of one to 10 carbons, and aliphatic hydrocarbon ketones of threeto 10 carbons.

2. The process of claim 1 wherein the reaction temperature is from 35 toC.

3. The process of claim 1 wherein the cosolvent is acetic acid or methylethyl ketone in a weight ratio to the sulfuric acid of 1:10 to :1.

4. The process of claim 1 wherein the para-substituted phenol is2,6-di-tert-butyl-p-cresol. 5

5. The process of claim 1 wherein the para-substituted phenol is2,4,6-tri-tert-butylphenol.

2. The process of claim 1 wherein the reaction temperature is from 35*to 90* C.
 3. The process of claim 1 wherein the cosolvent is acetic acidor methyl ethyl ketone in a weight ratio to the sulfuric acid of 1:10 to10:1.
 4. The process of claim 1 wherein the para-substituted phenol is2,6-di-tert-butyl-p-cresol.
 5. The process of claim 1 wherein thepara-substituted phenol is 2,4,6-tri-tert-butylphenol.